(a) Field of the Invention
The present invention relates to a method and an apparatus for virtualizing an antenna in a multi-antenna system, and a method and apparatus for transmitting/receiving a signal using the same.
(b) Description of the Related Art
A multiple-input multiple-output (MIMO) method is a method of transmitting and receiving a signal by using a plurality of transmission antennas and a plurality of reception antennas. In the MIMO system, a plurality of radio channel paths are generated between the transmission/reception antennas, and data transmission capacity is increased and performance may be improved by separating or merging them to transmission/reception end. The MIMO technique includes a spatial multiplexing method and a spatial diversity technique.
Also, the MIMO technique may be classified into a closed-loop technique and an open-loop technique depending on channel state information (CSI) feedback existence. The closed-loop technique is a technique in which pre-coding in a transmission end depends on the CSI feedback of the terminal, and the open-loop technique is a technique in which pre-coding in the transmission end does not depend on the CSI feedback of the terminal.
Various downlink and uplink MIMO techniques have been introduced in the LTE (long term evolution) system. The downlink MIMO technique supports transmit diversity, cyclic delay diversity (CDD), closed-loop beamforming, and spatial multiplexing methods. Also, the downlink MIMO technique supports a multi-user MIMO (MU-MIMO) technique of simultaneously transmitting data to a plurality of terminals in the same resource. Four transmission antennas are defined as a maximum in LTE Release 8, and eight transmission antennas are defined as a maximum in LTE Release 10.
In the LTE standard, an antenna port (AP) as a logical antenna unit is realized by a weighted sum of one or a plurality of physical antenna elements and is mainly defined in the transmission end. The antenna port is also a basic unit in which an LTE reference signal(s) (RS) is transmitted. Accordingly, the terminal estimates a channel for each antenna port that is not the physical antenna element and performs CSI measuring and reporting based on the channel. Different antenna port numbers are respectively given to a cell-specific RS (CRS), a user equipment-specific RS (URS), and a CSI-RS that are LTE downlink reference signals. For example, the antenna port number for the CRS may be #0 to #3, the antenna port number for the URS may be #7 to #14, and the antenna port number for the CSI-RS may be #15 to #22 . Mapping between the antenna port and the physical antenna element(s) is referred to as antenna virtualization. Basically, the terminal cannot know whether any virtualization is applied to each antenna port.
On the other hand, when the base station configures CSI-RS antenna ports of a large number to the terminal, a method for ensuring maximum transmission power for each CSI-RS antenna port is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.